1. Field of the Invention
The invention relates to systems and methods for controlling a vehicle engine.
2. Background Discussion
An engine of an alternatively powered vehicle (e.g., a hybrid electric vehicle), may drive a compressor of the vehicle's air conditioning system such that when the engine if off, the compressor is off. In a hybrid electric vehicle the engine is off when the vehicle is powered solely using electric power. The compressor may be operated by turning the engine on such that an occupant-selected desired temperature is achieved when the vehicle is in the electric power drive mode or when the vehicle is not moving.
Determining whether to start the engine if it is off may depend on an interior condition, e.g., cabin temperature, of the vehicle. If the interior condition exceeds a threshold condition that is based on the desired temperature, the engine may be started so the compressor can operate.
The air conditioning system may be configured to allow an occupant of the vehicle to select between a first mode and a second mode. In the first mode, if the interior condition exceeds the threshold condition and the engine is off, the engine will remain off. This strategy may improve fuel economy but an occupant may perceive or feel discomfort. In the second mode, if the interior condition exceeds the threshold condition and the engine is off, the engine will be started. This strategy may prevent an occupant from perceiving or feeling discomfort but may reduce fuel economy. An occupant may be willing to tolerate uncomfortable threshold conditions in an effort to improve fuel economy.
A system and method are desired for controlling an engine to drive a compressor of a vehicle air conditioning system so that an occupant may selectively determine interior conditions for a given ambient condition.